1. Field of the Invention
The present invention relates to a centrifugal blower.
2. Description of the Related Art
A centrifugal blower has an impeller, a casing that houses this impeller and forms a spiral flow passage around the radial direction outside of the impeller, and a driving device that rotates the impeller about the axis thereof. In the centrifugal blower the impeller is rotated by the driving device to impart a centrifugal force to the gas that has been taken into the casing and force feeding it into the flow passage. Air is supplied from the impeller to the spiral flow passage sequentially from a start point to a downstream side. Therefore, the internal pressure at the start point of the spiral flow passage is lowest and the internal pressure becomes higher close to the downstream side. The portion of the spiral flow passage one circle from the start point is adjacent to the start point, where the internal pressure is lowest. As a result, the internal pressure of the spiral flow passage in the vicinity of a border section one circle from the start point, (hereinafter referred to as the “nose section”), is close to that at the start point.
Such a centrifugal blower is used as an air blower for a vehicle air conditioning apparatus as in the multi-vane air blower disclosed in Patent Document 1 mentioned later for example.
The impeller has: a disk shaped bottom plate that is rotated about its axis by a driving device; a large number of blades provided projecting in the axial direction on the same circumference of this bottom plate; and a substantially annular plate shape shroud disposed concentric with the bottom plate, and having the blades interposed between it and the bottom plate, and being joined to the end part of each blade.
In the casing, there is provided a bell-mouth that opposes the area on the radially inside of the shroud to serve as an air intake. The air that has been supplied to the bell-mouth is imparted with a centrifugal force by rotating the impeller, and then force fed into the flow passage.
Patent Document 1:
Japanese Unexamined Patent Application, Publication, No. Hei 7-27097